Method and apparatus for detecting backside contamination during fabrication of a semiconductor wafer

ABSTRACT

A method of detecting contamination on a backside of a semiconductor wafer includes the steps of positioning the backside of the wafer in contact with a detection surface of a contaminant sensor, and detecting deformation of the detection surface of the contaminant sensor. The contaminant sensor may be incorporated into a fabrication device such as a wafer handling device, or can be utilized in the construction of a stand-alone device. An apparatus for detecting contamination on the backside of a semiconductor wafer is also disclosed.

This application is a divisional application of U.S. patent applicationSer. No. 10/138,742 which was filed on May 3, 2002 and now U.S. Pat. No.6,627,466 is incorporated herein by reference.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates generally to semiconductor waferfabrication, and more particularly to a method and apparatus fordetecting backside contamination during fabrication of a semiconductorwafer.

BACKGROUND OF THE DISCLOSURE

Semiconductor integrated circuits are typically fabricated by a layeringprocess in which several layers of material are fabricated on a surfaceof a wafer. Contamination on the backside of the wafer (i.e., the sideof the wafer opposite to the surface being layered) is a significantcontributor to problems during fabrication. In particular, contaminationon the backside of the wafer may cause fabrication defects at a numberof different processing steps. For example, the presence of backsidecontamination may cause over etching or under etching during thechemical etching process or during the chemical-mechanical polishingprocess (CMP). Moreover, the presence of backside contamination may alsocause imaging-related defects during process steps such asphotolithography, wafer inspection, or during rapid thermal annealing(RTA). Backside contamination may also be the cause of poor surfacecontact with the backside of the wafer during processes which utilize RFor heat transfer to the backside of the wafer such as during the etchingprocess or RTA.

Large contamination particles may even be undesirably transferred to thefront side of the wafer thereby potentially causing scratching of thefront side of the wafer or the “micromasking” of a portion of the frontside of the wafer. In some extreme cases, the presence of backsidecontamination may even cause wafers to be broken due to stress or lossof vacuum pressure during wafer handling.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the present disclosure, there isprovided a method of fabricating a semiconductor wafer. The methodincludes the steps of positioning the wafer in a wafer handling device,and detecting presence of a contaminant on a backside of the wafer whilethe wafer is positioned in the wafer handling device.

In accordance with another aspect of the present disclosure, there isprovided an apparatus for fabricating a semiconductor wafer. Theapparatus includes a wafer handling device. A contaminant sensor issecured to the wafer handling device. The contaminant sensor isconfigured to detect presence of a contaminant on a backside of thewafer when the wafer is positioned in the wafer handling device.

In accordance with a further aspect of the present disclosure, there isprovided a method of detecting contamination on a backside of asemiconductor wafer. The method includes the steps of positioning thebackside of the wafer in contact with a detection surface of acontaminant sensor, and detecting deformation of the detection surfaceof the contaminant sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 are cross sectional views of a semiconductor wafer duringvarious steps of a wafer fabrication process;

FIG. 7 is a cross sectional view of contaminant sensor being utilized todetect presence of a contaminant on the backside of a semiconductorwafer;

FIG. 8 is an enlarged view similar to FIG. 7, but showing a specificexemplary embodiment of a contaminant sensor; and

FIG. 9 is a diagrammatic cross sectional view which shows a contaminantsensor integrated into a wafer handling device.

DETAILED DESCRIPTION OF THE DISCLOSURE

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit thedisclosure to the particular forms disclosed, but on the contrary, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the disclosure as defined by theappended claims.

Referring now to FIGS. 1-6, there is shown a semiconductor wafer 10during various steps of a fabrication process. The semiconductor wafer10, as shown in FIGS. 1 and 2, includes a semiconductor substrate 12,such as silicon. A first insulating layer 14 and a first metal layer 16are deposited or otherwise disposed on the semiconductor substrate 12.In particular, the fabrication process deposits the first insulatinglayer 14 on the semiconductor substrate 12 such that a contact hole 18is formed in the first insulating layer 14 at a location above atransistor portion of the semiconductor substrate 12. Moreover, thefabrication process patterns the first metal layer 16 over the firstinsulating layer 14 and the contact hole 18. As a result, the firstmetal layer 16 fills the contact hole 18 forming an electrical contactwith the transistor portion of the semiconductor substrate 12. Moreover,the filling of the contact hole 18 forms a pit 20 in the portion of thefirst metal layer 16 disposed above the contact hole 18.

As shown in FIG. 3, a second insulating layer 22 is deposited on theouter surface of the first insulating layer 14 and the first metal layer16. The second insulating layer 22 has an uneven surface topography as aresult of the varying topography associated with the first insulatinglayer 14 and a first metal layer 16. A polishing process such as achemical-mechanical polishing (CMP) process may be utilized to polishthe second insulating layer 22 down to a desired level 24 therebyplanarizing the surface of the second insulating layer 22 (see FIG. 1D).

As alluded to above, once the semiconductor wafer 10 has been polishedsuch that a planar surface is created, additional layers may bedeposited or otherwise fabricated thereon. For example, as shown inFIGS. 5 and 6, a via hole 26 may be patterned via a lithography processand thereafter formed through the second insulating layer 22 via anetching process. Thereafter, a second metal layer 28 may be deposited onthe second insulating layer 22. It should be appreciated that numerousadditional layers may be deposited on the semiconductor wafer 10 in themanner previously described.

During such a wafer fabrication process, along with wafer fabricationprocesses having numerous additional or fewer process steps,contamination can accumulate on a backside 30 of the semiconductor wafer10. Such contamination may take on many forms such as particles, debris,or the like that accumulate on the backside 30 of the semiconductor 10as a result of the numerous process and handling steps.

As shown in FIG. 7, a contaminant sensor 32 may be utilized to detectpresence of a contaminant 34 on the backside 30 of the semiconductorwafer 10. The contaminant sensor 32 may be any type of sensing devicefor sensing presence of contaminants of the size typically associatedwith wafer fabrication. In illustrative embodiments, the contaminantsensor 32 is embodied as a pressure sensing film which senses pressurechanges (e.g., pressure increases) as a result of deflection ordeformation of an outer surface thereof. Specifically, the pressuresensing film used in the construction of the contaminant sensor 32 maybe configured to sense two distinct states. In the case of when thebackside 30 of the wafer 10 is devoid of contamination 34, an evencompression is present across the film. However, when an outer detectionsurface 36 of the film deflects or otherwise deforms as a result ofcontamination 34 being trapped between the contaminant sensor 32 and thebackside 30 of the semiconductor wafer 10, a local pressure will becreated in the pressure sensing film. Presence of this local pressuretriggers the sensor 32.

In such a way, the sensor 32 senses deflection or deformation of thedetection surface 36 and generates an output signal indicative thereof.The output signal generated by the contaminant sensor 32 may be utilizedby one or more control systems associated with the wafer fabricationprocess. For instance, the control system associated with a waferhandling device may utilize the output signal from the contaminantsensor 32 to determine whether the wafer 10 is to be advanced to, forexample, (i) a subsequent processing step in the case of when the waferis devoid of backside contamination, or (ii) an offline rework stationin the case of when contamination is detected on the backside 30 of thewafer 10.

Similarly, the wafer loader associated with a piece of fabricationequipment may be equipped with a contamination sensor 32 to monitor theoutput signals therefrom to determine if backside contamination ispresent on the wafer prior to commencement of the process beingperformed by the equipment. Conversely, the wafer unloader associatedwith a piece of fabrication equipment may be equipped with acontamination sensor 32 to monitor the output signals therefrom todetermine if backside contamination was introduced onto the wafer duringthe process being performed by the equipment.

As described herein, the contaminant sensor 32 may embodied as a numberof different types of pressure sensitive films. For example, thecontaminant sensor 32 may be embodied as a thin pressure sensing filmthat includes one or more micro strain gauges. Such a thin film may beconfigured to sense changes in pressure across the entire area of thefilm. Alternatively, the film may be configured in a grid-like patternthereby producing a number of smaller, local sensing areas. In thismanner, several distinct areas of the backside 30 of the wafer 10 may bemonitored to produce data indicative of the density, size, and locationof the backside contaminants.

The thin pressure sensing film may also be configured as a liquidcrystal film. In such a configuration, a liquid crystal media isinterposed between a light source and a light receptor. Deformation ordeflection of the liquid crystal media distorts the transmission oflight generated by the light source through the media, with suchdistortion being detected by the light detector. This phenomena isexemplified by pressing or otherwise applying pressure to the outersurface of a liquid crystal display screen such as the display screentypically associated with a laptop computer.

The pressure sensing film may also be configured as the multi-layeredfilm assembly 46 shown in FIG. 8. In particular, the contaminant sensor32 may be constructed to include a pair of conductive films 40, 42, witha dielectric film 44 therebetween. In such a configuration, the sensingsurface 36 is defined in the conductive film 40. A “base” capacitance ofthe film assembly 46 may be determined based on the stored charge in the“gap” between the conductive films 40, 42 created by the dielectric film44. When contamination 34 is present on the backside 30 of the wafer 10,the conductive film 40 is deflected, deformed, or otherwise urged in thegeneral direction of the conductive film 42 thereby changing the widthof the gap between the two films 40, 44. This change in width of the gapchanges the capacitance of the assembly. Such a change is capacitance isdetected by the contamination sensor 32 thereby causing the sensor 32 togenerate an output signal for use by a system controller in the mannerdescribed above.

As alluded to above, the contaminant sensors of the present disclosuremay be utilized in a number of different manners within the waferfabrication process. For example, as shown in FIG. 9, the contaminantsensor 32 may be incorporated into a wafer handling device 50 such as aprocessing chuck, an alignment apparatus, a wafer handler such as a loadfork or the like. In such a case, as shown in FIG. 9, the sensor 32 isinterposed between a support surface 52 of the wafer handling device 50and the backside 30 of the wafer 10. Alternatively, in lieu ofintegration into an existing apparatus, the contaminant sensor 32 may beincorporated into a “stand alone” device which is operated for thepurpose of detecting backside contamination.

While the concepts of the present disclosure has been illustrated anddescribed in detail in the drawings and foregoing description, suchillustration and description is to be considered as exemplary and notrestrictive in character, it being understood that only exemplaryembodiments have been shown and described and that all changes andmodifications that come within the spirit of the concepts of the presentdisclosure are desired to be protected.

There are a plurality of advantages of the concepts of the presentdisclosure arising from the various features of the apparatus andmethods described herein. It will be noted that alternative embodimentsof the apparatus and methods of the present disclosure may not includeall of the features described yet still benefit from at least some ofthe advantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations of the apparatus and methods ofthe present disclosure that incorporate one or more of the features ofthe present disclosure and fall within the spirit and scope of theinvention defined by the appended claims.

1. An apparatus for fabricating a semiconductor wafer, comprising: awafer handling device, and a contaminant sensor secured to the waferhandling device, the contaminant sensor being configured to detectpresence of a contaminant on a backside of the wafer when the wafer ispositioned in the wafer handling device, wherein the contaminant sensorcomprises a deformable detection surface configured to contact thebackside of the wafer when the wafer is positioned in the wafer handlingdevice.
 2. The apparatus of claim 1, wherein: the contaminant sensor isconfigured to output (i) a first control signal indicative of a firstcapacitance value when the backside of the wafer is devoid ofcontaminant particles, and (ii) produce a second control signalindicative of a second capacitance value when a contaminant particle ispresent on the backside of the wafer, and the first control signal isdifferent from the second control signal.
 3. The apparatus of claim 1,wherein the contaminant sensor comprises a first conductive film, asecond conductive film, and a dielectric film positioned between thefirst conductive film and the second conductive film.
 4. The apparatusof claim 3, wherein the first conductive film is configured to contactthe backside of the wafer when the wafer is positioned in the waferhandling device.
 5. The apparatus of claim 1, wherein the contaminantsensor comprises a pressure sensing film.
 6. The apparatus of claim 1,wherein the contaminant sensor comprises a liquid crystal film.